Energy storage device
By optimizing the solvent ratio of the electrolyte and adding film-forming additives, a lithium-ion battery electrolyte suitable for a wide temperature domain was prepared, which solved the problem of insufficient performance of the existing electrolyte in a wide temperature domain and achieved good energy storage performance in a wider temperature range.
Patent Information
- Application Number
- CN202510026652.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Priority Date
- 2024-01-28
- Filing Date
- 2025-01-08
- Publication Date
- 2025-04-11
AI Technical Summary
The electrolytes of existing hybrid energy storage devices show insufficient low-temperature performance and high-temperature performance in a wide temperature range, and cannot meet the needs of wider temperature ranges in military and aerospace fields.
By optimizing the solvent type and ratio of the electrolyte and combining with an appropriate amount of film-forming additive, a wide temperature domain electrolyte of lithium-ion battery is prepared. The specific steps include mixing vinyl carbonate, ethyl butyrate and methyl ethyl carbonate as solvents, adding lithium hexafluorophosphate and lithium tetrafluorophosphate as lithium salts, and finally adding tetraethoxysilane as film forming additives.
The electrolyte exhibits better performance in the temperature range of -30°C to 55°C, including higher capacity retention and better cycling performance, and can meet a wider range of environmental conditions.
Smart Images
Figure CN119812487A_ABST
Abstract
Description
Technical Field
[0001] The invention relates to the field of electrochemical technology, and in particular to an energy storage device. Background Art
[0002] Hybrid energy storage devices are a new type of energy storage system, including hybrid supercapacitors, hybrid battery capacitors and / or other hybrid battery components. They combine the material intercalation chemical energy storage mechanism of ion batteries and the physical energy storage idea of adsorption and desorption of porous large specific surface area activated carbon of supercapacitors. In terms of performance, their energy density and power are between ion batteries and supercapacitors, and they have deep research significance and broad application prospects.
[0003] However, there are many shortcomings in the electrolytes suitable for hybrid energy storage devices. The application field of energy storage devices is significantly affected by their operating temperature. The operating temperature of the power battery of electric vehicles is generally -20 to 60°C, while the military and aerospace fields require a wider operating temperature range. The operating temperature range required in the military industry is -40 to 55°C. The wide temperature range electrolyte needs to have both good low-temperature performance and high-temperature performance. In a low-temperature environment, the internal reaction of the energy storage device is a reversible process, which is mainly limited by the diffusion rate. As the temperature decreases, the surface film resistance of the positive and negative electrodes, the bulk resistance of the electrolyte, and the charge transfer resistance will increase significantly; in a high-temperature environment, the reaction rate of the components in the electrolyte on the surface of the positive and negative electrode materials is accelerated, the stability of the interface film deteriorates, and the electrolyte will also undergo decomposition reactions at high temperatures.
[0004] At present, the research on expanding the operating temperature range of lithium-ion batteries mainly starts from two aspects: one is to develop solid electrolytes, and the other is to optimize the current liquid electrolyte system. However, the development of solid electrolytes is still in the optimization stage, and most research results are still in the laboratory stage, which is still a long way from commercial application. For the optimization of liquid electrolytes, most of them are only for high or low temperatures. Although they have good effects for a single use environment, they still cannot meet the application requirements in special scenarios with drastic temperature changes. ]
[0005] At present, the research and development of wide temperature range electrolytes mainly focuses on three aspects: lithium salts, co-solvents and functional additives. (1) The influence of lithium salts is mainly reflected in the stability under high temperature environment and the lithium ion conductivity under low temperature environment. The lithium salts currently used in lithium-ion batteries are mainly LiPF6, LiClO4, LiBF4, LiAsF6, Li(CF3SO2)2N, etc. Among them, LiPF6 is the most widely used, but LiPF6 has poor thermal stability and will decompose significantly above 60°C; LiClO4 itself has good thermal stability, but the chlorine in it is in a high oxidation state, and it is easy to react strongly with organic solvents under some extreme conditions (such as high temperature, high current density, etc.), bringing safety hazards; LiBF4 has good low temperature conductivity. (2) The solvents currently used mainly include carbonates, ethers, amides and sulfones. Ethers have a low oxidation potential and are not suitable for high-voltage batteries. Sulfones have a high melting point and poor low temperature performance, so they are not suitable for wide temperature range electrolytes. Among carbonate solvents, cyclic carbonate EC (ethylene carbonate) can participate in the formation of SEI film, ensure the stability of the electrolyte and negative electrode interface, and has certain benefits for high temperature performance, while linear carbonate DEC (diethyl carbonate), DMC (dimethyl carbonate), and EMC (ethyl methyl carbonate) have lower freezing points and have better performance in low temperature environments. (3) Functional additives mainly include film-forming additives, lithium salt stabilizers, and positive electrode stabilizers. For example, film-forming additives mainly react with the negative electrode before other components in the electrolyte to generate SEI film on the negative electrode, prevent further redox reactions, and improve battery stability.
[0006] Current research and development of electrolytes is mostly aimed at high or low temperatures alone, while research and development of electrolytes with a wide temperature range is relatively rare. The large temperature difference between different regions in the world affects the further development of electric vehicles. Therefore, the development of electrolytes suitable for a wide temperature range is of great significance for improving battery performance, deeply tapping battery potential, and promoting the further expansion of the electric vehicle market.
[0007] Based on this, a new technical solution is needed to provide a low-cost, easy-to-prepare, and relatively good performance wide temperature range electrolyte design, and to assemble a new hybrid energy storage device. The low-temperature performance can be improved by optimizing the type and ratio of solvents, and the high-temperature performance can be improved by adding an appropriate amount of film-forming additives, so as to ensure that the energy storage device has good performance in a wider temperature range. Summary of the invention
[0008] The purpose of the present invention is to provide an energy storage device to solve the above problems in the prior art.
[0009] In order to solve the above problems, according to one aspect of the present invention, a method for preparing a lithium ion battery wide temperature range electrolyte is provided, characterized in that the method for preparing the lithium ion battery wide temperature range electrolyte comprises the following steps:
[0010] Step 1: Mix ethylene carbonate EC, ethyl butyrate EB and ethyl methyl carbonate EMC in a volume ratio of 1:1:1-1:1:3, and stir until the three solvents are completely miscible;
[0011] Step 2: Cool the mixture obtained in step 1 to 10°C;
[0012] Step 3: Add lithium hexafluorophosphate LiPF6 to the solution cooled in step 2, with the volume ratio of lithium hexafluorophosphate LiPF6 to ethylene carbonate EC being 1:4 to 1:7, and stir until the components in the solution are completely dissolved in each other and become clear and transparent;
[0013] Step 4: Add tetraethoxysilane TEOS to the solution obtained in step 3 in a volume ratio of 1:7 to 1:9 to ethylene carbonate EC, and stir until the components in the solution are completely miscible and clear and transparent.
[0014] In a preferred embodiment of the present invention, the method for preparing a wide temperature range electrolyte for lithium-ion batteries also includes step five: heating the mixed solution obtained in step four to 25°C, and adding vinyl carbonate (VC), vinyl sulfate (DTD) and fluoroethylene carbonate (FEC) in a volume ratio of 1:2:3-3:2:1 in sequence.
[0015] The present invention also provides an energy storage device, comprising a positive electrode, a negative electrode, a diaphragm and an electrolyte, wherein the electrolyte is prepared by the above-mentioned electrolyte preparation method, the positive electrode material is a lithium oxide mixed nanoporous activated carbon, the negative electrode material is an amorphous carbon-based material hard carbon or soft carbon, the mass ratio of lithium tetrafluorophosphate (LiBF4) and lithium hexafluorophosphate (LiPF6) in the lithium salt is 2:8, and in the step one, a magnetic particle is used to stir at a speed of 100 to 200 r / min for 1.5 h to 2 h until the three solvents are completely miscible and no stratification occurs.
[0016] In a preferred embodiment of the present invention, in the step three, the concentration of the mixture of lithium tetrafluorophosphate (LiBF4) and lithium hexafluorophosphate (LiPF6) in the lithium salt is 1 mol / L.
[0017] In a preferred embodiment of the present invention, in step three, the rotation speed of the magnet is 200-300 r / min.
[0018] In a preferred embodiment of the present invention, in the step 4, the mass fraction of tetraethoxysilane (TEOS) is 0.5%, and the rotation speed of the magnet is 200-300 r / min.
[0019] In a preferred embodiment of the present invention, in the step five, vinylene carbonate (VC), vinyl sulfate (DTD) and fluoroethylene carbonate (FEC) are added in sequence respectively, which needs to be carried out in 5 times, and the interval time of each time is controlled at 6 to 8 minutes, and the stirring speed is controlled at 300r / min.
[0020] In a preferred embodiment of the present invention, in the step 1, the volume ratio of ethylene carbonate (EC), ethyl butyrate (EB) and ethyl methyl carbonate (EMC) is 1:1:2, and in the step 5, the volume ratio of vinylene carbonate (VC), vinyl sulfate (DTD) and fluoroethylene carbonate (FEC) is 1:1.2:1.5.
[0021] In a preferred embodiment of the present invention, steps 1 to 5 are all performed in a glove box, and the oxygen concentration and water concentration are both less than 0.01 ppm.
[0022] In a preferred embodiment of the present invention, the separator is high molecular weight polyethylene and polypropylene.
[0023] The positive electrode of the hybrid capacitor system of the present invention is a mixed nanoporous activated carbon containing lithium oxide, and the negative electrode is an amorphous carbon-based material hard carbon / soft carbon. The energy storage mechanism of activated carbon is mainly based on the adsorption and desorption of anions and cations, and energy is stored by relying on the double electric layer effect generated at the interface between the electrode material and the electrolyte. The main factors affecting the performance of activated carbon: the larger the effective specific surface area, the higher the specific capacity in theory. The effective specific surface area refers to the specific surface area of the electrode material in contact with the electrolyte, which involves the pore size distribution. A good pore size distribution can increase the effective specific surface area. The positive electrode contains lithium oxide to provide lithium ion extraction / embedding. Based on the intercalation electrochemical energy storage mechanism of lithium-ion batteries, the positive electrode introduces the activated carbon adsorption and desorption energy storage mechanism to form a high-power and long-life positive electrode system. The negative electrode is mainly hard carbon. Compared with graphite (0.335nm), the distorted carbon layer structure of hard carbon increases the repulsive force between graphitized carbon layers, so that it has a larger interlayer spacing (~0.38nm). This large interlayer spacing and nanopores are also conducive to the diffusion of ions and the stability of the structure during the cycle. In addition, heteroatoms in the carbonization process will also form defect sites in the carbon layer. In addition to the graphite domain, there are a large number of vacancies, edges and defect sites in the hard carbon structure, which makes hard carbon a highly competitive high-power negative electrode. Based on the system mechanism of hybrid capacitors, the current electrolyte selection is mainly based on lithium-ion high-power battery electrolytes, and no highly adaptable special electrolytes have been formed.
[0024] Compared with the prior art, the beneficial effects that can be achieved by at least one of the above-mentioned technical solutions adopted in the embodiments of this specification include at least the following: At present, the research and development of wide temperature range electrolytes mainly focuses on three aspects: ① Electrolyte lithium salts, the high temperature resistant lithium salts that are of great concern are mainly lithium borate complexes and lithium phosphate complexes, such as LiBOB and LiTFSI; ② Wide temperature range co-solvents, cyclic carbonates have high ionic conductivity and can form a SEI film on the negative electrode, which has certain benefits for high temperature performance. Linear carbonates such as DEC, DMC, EMC, etc. have low freezing points and viscosities, which can reduce the viscosity of the electrolyte as a whole, which is of great significance for the expansion of the low temperature field of the electrolyte; ③ Functional additives, mainly including SEI film additives and positive electrode protection additives, among which EC is both a SEI film forming additive and a positive electrode protection additive.
[0025] The present invention is based on the actual situation, by optimizing the type and ratio of electrolyte co-solvents, while ensuring the electrolyte has high ionic conductivity and low viscosity, and broadens the low temperature performance of the electrolyte as much as possible. At the same time, the appropriate amount of co-solvent EC plays a certain protective role on the ternary nickel-cobalt-manganese positive electrode, and helps to form the negative electrode graphite SEI film. The addition of an appropriate amount of high temperature additives also helps to improve the high temperature performance of the electrolyte, thereby broadening the high and low temperature range of the electrolyte as a whole.
[0026] In order to achieve greater performance, the present invention specially adds multi-component electrolyte additives such as vinylene carbonate (VC), diethylene sulfate (DTD), and fluoroethylene carbonate (FEC), and cooperates with various additives to comprehensively improve the electrochemical performance to meet commercial application requirements.
[0027] The wide temperature range electrolyte solution proposed in the present invention is suitable for a wider temperature range. Compared with the electrolyte of 1mol.L-1LiPF6EC / DEC / DMC (1:1:1), it shows better performance in the temperature range of -30-55°C. At 55°C, there is no obvious gas production phenomenon, the voltage retention rate is good, and the cycle capacity retention rate is also good. The discharge capacity of the lithium primary battery injected with the wide temperature range electrolyte in the embodiment of the present invention exceeds the rated capacity at room temperature under 55°C, reaching 105% of the capacity at room temperature. This is mainly because the internal resistance of the battery is reduced as the temperature increases; and 95% of the capacity at room temperature is released under -30°C, indicating that the electrolyte exhibits excellent high and low temperature performance in the lithium primary battery system. At the same time, the wide temperature range electrolyte prepared in this embodiment has excellent electrical properties in different temperature ranges, can be discharged at a rate of 1C in lithium metal oxide secondary batteries, and exhibits good electrical properties in the range of -30°C to 55°C, that is, high capacity retention rate and good cycle performance.
[0028] At the same time, from the perspective of preparation method, the wide temperature range electrolyte solution proposed in the present invention has a simple preparation method, fewer operating procedures, and the selected lithium salts, co-solvents and functional additives are easy to obtain and the cost is relatively low.
[0029] The present invention starts with co-solvents and functional additives at the same time, and takes a two-pronged approach to improve the performance of the electrolyte under wide temperature range conditions. The low-temperature performance of the electrolyte is improved by selecting the type of co-solvent and optimizing the proportion, selecting linear carboxylates with low freezing point, low viscosity and good low-temperature conductivity, and appropriately reducing the proportion of ethylene carbonate (EC). On the other hand, adding an appropriate amount of the functional additive tetraethoxysilane (TEOS) can react on the surface of the ternary nickel-cobalt-manganese positive electrode to generate an interface layer with low impedance, which protects the positive electrode at high temperature and improves the high-temperature performance of the energy storage device. BRIEF DESCRIPTION OF THE DRAWINGS
[0030] Figure 1 Schematic diagram of energy storage device.
[0031] Figure 2 Schematic diagram of the preparation process of wide temperature range electrolyte.
[0032] Figure 3 This is the discharge curve of the soft-pack metal oxide lithium battery (NCM / / Gr) injected with the wide temperature range electrolyte prepared in an embodiment of the present invention at 55°C; the discharge capacity of the lithium primary battery of the wide temperature range electrolyte of the present invention exceeds the rated capacity at room temperature at 55°C, reaching 105% of the capacity at room temperature, which is mainly because the internal resistance of the battery is reduced as the temperature increases.
[0033] Figure 4 The discharge curve of the soft-pack metal oxide lithium battery (NCM / / Gr) injected with the wide temperature range electrolyte prepared in an embodiment of the present invention at -30°C; 95% of the room temperature capacity was released under -30°C conditions, indicating that the electrolyte exhibits excellent high and low temperature performance in the lithium primary battery system.
[0034] Figure 5 It is a curve comparison of the discharge capacity of the wide temperature range low-temperature electrolyte prepared in the embodiment of the present invention and the 1M LiPF6 EC / DMC injected soft-pack metal oxide secondary battery (NCM / / Gr) at -30°C. The discharge rate is 1C. Compared with the conventional electrolyte, the low-temperature discharge curve of the wide temperature range electrolyte is flat and releases 95% of the effective capacity. At the low temperature of -30°C, the conventional electrolyte has an abnormal curve, severe polarization and voltage offset in the initial section, indicating that it does not meet the low-temperature discharge conditions, and the actual discharge releases less than 50% of the effective capacity.
[0035] Figure 6 The DC internal resistance data of the trial samples with different volume ratios of tetraethoxysilane to tetraethoxysilane are shown in Figure 2. DETAILED DESCRIPTION
[0036] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings so that the purpose, features and advantages of the present invention can be more clearly understood. It should be understood that the embodiments shown in the accompanying drawings are not intended to limit the scope of the present invention, but are only intended to illustrate the essential spirit of the technical solution of the present invention.
[0037] In the following description, certain specific details are set forth for the purpose of illustrating the various disclosed embodiments to provide a thorough understanding of the various disclosed embodiments. However, those skilled in the relevant art will recognize that the embodiments may be practiced without one or more of these specific details. In other cases, well-known devices, structures, and techniques associated with the present application may not be shown or described in detail to avoid unnecessarily obscuring the description of the embodiments.
[0038] References throughout the specification to "one embodiment" or "an embodiment" indicate that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of "in one embodiment" or "in an embodiment" in various places throughout the specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any manner in one or more embodiments.
[0039] In the following description, in order to clearly show the structure and working mode of the present invention, many directional words will be used for description, but the words "front", "back", "left", "right", "outside", "inside", "outward", "inward", "up", "down", etc. should be understood as convenient terms and should not be understood as restrictive terms.
[0040] It should be noted that the features shown in the drawings of the present application may belong to one embodiment or to different embodiments, as long as there is no conflict between these features. In order to save space, the present application may use the same drawing to illustrate different embodiments, that is, the same drawing of the present application may be used to reflect the features in different embodiments.
[0041] like Figure 1 An energy storage device 10 shown includes a positive electrode 11, a negative electrode 13, a separator 12 and an electrolyte. The single cell 10 includes a positive electrode current collector 11, a negative electrode current collector 13 and a separator 12. The positive electrode is coated with a positive electrode active material 15, which is a lithium oxide mixed nanoporous activated carbon. The negative electrode 13 is coated with a negative electrode active material 14, which is an amorphous carbon-based material hard carbon or soft carbon. The energy storage device 10 is filled with an electrolyte.
[0042] like Figure 2As shown, the preparation method of the wide temperature range electrolyte of the energy storage device of the present invention comprises the following steps: Step 1: Ethylene carbonate (EC), ethyl butyrate (EB) and ethyl methyl carbonate (EMC) are mixed in a volume ratio of 1:1:1-1:1:3, preferably 1:1:2, and stirred with a magnetic stirrer at a speed of 100-200 r / min for 1.5h-2h until the three solvents are completely miscible and no stratification occurs.
[0043] Step 2: Cool the mixture obtained in step 1 to 10°C.
[0044] Step 3: Add a mixture of lithium tetrafluorophosphate (LiBF4) and lithium hexafluorophosphate (LiPF6) to the solution cooled in step 2, wherein the concentration of the mixture is 1 mol / L, and the volume ratio of the mixture to ethylene carbonate (EC) is 1:4 to 1:7, and stir the mixture at a speed of 200-300 r / min for 1.5 h to 2 h until the components in the solution are completely dissolved in each other and become clear and transparent.
[0045] Step 4: Add tetraethoxysilane (TEOS) to the solution obtained in step 3, wherein the mass fraction of tetraethoxysilane (TEOS) is 0.5%, and the volume ratio of tetraethoxysilane (TEOS) to ethylene carbonate is 1:7 to 1:9. Tetraethoxysilane is used as a film-forming additive, and its main function is to form a stable, dense and efficient SEI solid electrolyte film on the surface of the negative electrode, such as Figure 6 As shown, the sample with a volume ratio of 1:7 has low DC internal resistance and good consistency, making it the preferred solution. The internal resistance of 1:8 is relatively high, and the internal resistance of 1:9 is high and dispersed, because the high concentration of film-forming additives blocks the ion channel and affects ion diffusion); after adding tetraethoxysilane, stir until the components in the solution are completely dissolved, the speed of the magnet is 200-300r / min, and stir for 1.5h~2h until the components in the solution are completely dissolved and appear clear and transparent.
[0046] Step 5: The mixed solution obtained in step 4 is heated to 25°C, and vinylene carbonate VC, vinyl sulfate DTD, and fluoroethylene carbonate FEC are added in a volume ratio of 1:2:3-3:2:1 in sequence. The optimal ratio is 1:1.2:1. It needs to be carried out in 5 times, and the interval time of each time is controlled at 6-8 minutes, and the stirring speed is controlled at 300r / min.
[0047] The present invention designs the ratio of LiPF6:LiBF4 (8:2) in combination with the actual system. The solvents currently used mainly include carbonates, ethers, amides and sulfones. The oxidation potential of ethers is low and they are not suitable for high-voltage batteries. Sulfones have a high melting point and poor low-temperature performance, so they are not suitable for wide temperature range electrolytes. Among carbonate solvents, cyclic carbonate EC (ethylene carbonate) can participate in the formation of SEI film, ensure the stability of the electrolyte and the negative electrode interface, and have certain benefits for high-temperature performance, while linear carbonates DEC (diethyl carbonate), DMC (dimethyl carbonate), and EMC (ethyl methyl carbonate) have a lower freezing point and have better performance in low-temperature environments. The present invention mixes ethylene carbonate EC, ethyl butyrate EB and ethyl methyl carbonate EMC in a volume ratio of 1:1:2. By selecting the type of solvent and optimizing the proportion, linear carboxylates with low freezing point, low viscosity and good low-temperature conductivity are selected, and the proportion of vinyl carbonate (EC) is appropriately reduced to improve the low-temperature performance of the electrolyte; on the other hand, adding an appropriate amount of functional additive tetraethoxysilane (TEOS) can react on the surface of the positive electrode oxide to generate an interface layer with low impedance, which protects the positive electrode at high temperatures and improves performance; vinyl sulfate DTD can effectively reduce electrode polarization, increase the voltage platform, and promote the capacitor to exert higher energy at low temperatures; a small amount of vinyl carbonate VC will increase the conductivity of SEI and conduct Leading to the reduction of total anode impedance during Li embedding process, vinylene carbonate VC can not only improve the cycle life of the battery, but also improve the stability and low-temperature performance of the battery, and has a high value as an additive; the reasons why fluoroethylene carbonate FEC is used as an electrolyte additive are mainly: fluoroethylene carbonate has one more F bond in the molecule than ethylene carbonate, so its electronegativity and electron-withdrawing ability are stronger. Fluoroethylene carbonate is at a lower reduction potential during reduction, and a SEI film will be formed on the negative electrode surface at this time. The film has the characteristics of low resistance, so it can enhance the room temperature capacity, cycle stability and low temperature stability of the capacitor at the same rate.
[0048] Specifically, vinyl carbonate VC, as the first additive added, initially forms a SEI film on the surface of the negative electrode, laying the foundation for the construction of the SEI film. Subsequently, vinyl sulfate DTD is added, which, with its unique chemical properties, further stabilizes and optimizes the formation of the SEI film, forming a more uniform and dense film layer. The last added fluoroethylene carbonate FEC, with its special molecular structure, forms a layer of SEI film with low resistance and high stability on the surface of the negative electrode, which not only effectively protects the negative electrode material, but also significantly improves the cycle stability and low temperature performance of the battery. In terms of voltage platform and electrode polarization, vinyl sulfate DTD creates a favorable electrochemical environment for the subsequent formation of SEI film by reducing electrode polarization and improving voltage platform stability, while vinyl carbonate VC and fluoroethylene carbonate FEC jointly inhibit the polarization phenomenon of the battery by forming a stable SEI film. In addition, the synergistic effect of vinyl sulfate DTD and vinyl carbonate VC significantly improves the cycle stability of the battery, while fluoroethylene carbonate FEC further improves the low temperature performance of the battery. In terms of comprehensive performance, vinyl carbonate VC enhances the charge transfer efficiency of the battery by improving the conductivity of the SEI film; the fluorine atoms of fluoroethylene carbonate FEC reduce the resistance of the SEI film and improve the power output and energy efficiency of the battery; vinyl sulfate DTD improves the performance of the graphite negative electrode by optimizing the lithium solvation structure in the electrolyte, thereby improving the energy density of the battery. The design of this additive ratio not only optimizes the composition and structure of the SEI film, but also significantly improves the battery's cycle stability, low-temperature performance, energy density and power output. At the same time, the optimal volume ratio of vinyl carbonate VC and vinyl sulfate DTD of 1:1.2:1.5 can best suppress the polarization phenomenon of the battery.
[0049] The whole process of electrolyte preparation is in the glove box (H2O <0.01ppm, O2 <0.01ppm), the temperature is room temperature, ethylene carbonate (EC), ethyl butyrate (EB), ethyl methyl carbonate (EMC) are used as solvents, the volume ratio of the three is 1:1:1-1:1:3, the lithium salt is lithium hexafluorophosphate (LiPF6), the concentration is 1mol.L-1, and the additive is 0.5%wt tetraethoxysilane (TEOS), as shown in Table 1 below. The basic performance characterization of samples with different volume ratios mainly focuses on the ionic conductivity at +25℃ and -40℃. In the electrolyte solvent system, ions are conducted to the surface of the positive and negative active material particles. Ionic conductivity is the most important performance of the electrolyte. The electrolyte infiltrates between the positive and negative active material particles to construct a three-dimensional ionic conductive network at the positive and negative electrodes. The data show that the solvent system with a volume ratio of 1:1:2 has the best ionic conductivity and maintains a high electrochemical potential window.
[0050] Table 1 Basic performance characteristics of samples with the same volume ratio
[0051]
[0052] The operating temperature of the wide temperature range electrolyte is -30 to 55 ° C. Such an operating temperature enhances the environmental adaptability of lithium-ion batteries. The wide temperature range electrolyte can work normally at lower and higher temperatures, so it can adapt to a wider range of environmental conditions. Whether in extremely cold winter or hot summer, the electrolyte can maintain normal operation and will not fail due to temperature changes. At the same time, temperature changes may have a negative impact on the performance and life of systems such as electronic equipment and batteries. The use of wide temperature range electrolytes can reduce the risk of equipment failure at different temperatures and increase the reliability and stability of the system. Finally, due to the wide operating temperature range of wide temperature range electrolytes, it can be applied to more application scenarios. For example, automotive batteries need to operate normally in both severe winters and hot summers, and the use of wide temperature range electrolytes can meet this demand. In addition, some outdoor and industrial equipment also needs to be able to operate at extreme temperatures, and the characteristics of wide temperature range electrolytes make them a viable option.
[0053] A 1Ah soft pack was prepared using ternary nickel-cobalt-manganese (NCM) as the positive electrode and graphite (Gr) as the negative electrode. The test process was as follows: (1) Formation: Let stand for 5 min, charge at constant current to 4.2 V at 0.1C, charge at constant voltage until the current is ≤0.05C, discharge at constant current to 2.5 V at 0.1C, charge at constant current to 4.2 V at 1C, and let stand for 48 h.
[0054] (2) High and low temperature cycle test: Normal temperature cycle test, at 25℃±2℃, constant current charge and discharge are performed at a current density of 1C, the charge cut-off voltage is 4.2V, the discharge cut-off voltage is 2.8V, and the cycle is 300 cycles; low temperature cycle test, at -30℃±3℃, constant current charge and discharge are performed at a current density of 1C, the charge cut-off voltage is 4.2V, the discharge cut-off voltage is 2.5V, and the cycle is 300 cycles; high temperature cycle test, at 55℃±3℃, constant current charge and discharge are performed at a current density of 1C, the charge cut-off voltage is 4.2V, the discharge cut-off voltage is 2.8V, and the cycle is 300 cycles.
[0055] Experimental data such as Figures 3 to 5 As shown, the wide temperature range electrolyte prepared in this embodiment has excellent electrical properties at -30°C and 55°C, and can be discharged at a rate of 1C in a lithium metal oxide primary battery.
[0056] Depend on Figure 3 It can be seen that the discharge capacity of the lithium primary battery filled with wide temperature range electrolyte at 55°C exceeds the rated capacity at room temperature, reaching 105% of the capacity at room temperature. This is mainly because the internal resistance of the battery is reduced as the temperature increases. Figure 4In the experiment, 95% of the normal temperature capacity was released at -30°C, indicating that the electrolyte exhibits excellent high and low temperature performance in the lithium primary battery system.
[0057] The wide temperature range electrolyte prepared in this embodiment has excellent electrical properties in different temperature ranges and can be discharged at a rate of 1C in a lithium metal oxide secondary battery (e.g. Figure 4 shown).
[0058] It can be seen that the wide temperature range electrolyte shows good electrical properties in the range of -30℃ to 55℃, that is, high capacity retention rate; on the contrary, the conventional electrolyte 1M LiPF6 EC / DMC electrolyte fails to discharge in a low temperature environment, the curve is abnormal, and severe polarization and voltage offset occur in the initial section, indicating that it does not meet the low temperature discharge conditions, and the actual discharge releases less than 50% of the effective capacity.
[0059] In this specification, the same or similar parts between the various embodiments can be referred to each other, and each embodiment focuses on the differences from other embodiments. In particular, for the embodiments described later, the description is relatively simple, and the relevant parts can be referred to the partial description of the previous embodiments.
[0060] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.
Claims
1. A method for preparing a wide temperature range electrolyte for lithium-ion batteries, characterized in that: The method for preparing the wide temperature range electrolyte for lithium ion batteries comprises the following steps: Step 1: Mix ethylene carbonate EC, ethyl butyrate EB and ethyl methyl carbonate EMC in a volume ratio of 1:1:1-1:1:3, and stir until the three solvents are completely miscible; Step 2: Cool the mixture obtained in step 1 to 10°C; Step 3: Add lithium hexafluorophosphate LiPF6 to the solution cooled in step 2, with the volume ratio of lithium hexafluorophosphate LiPF6 to ethylene carbonate EC being 1:4 to 1:7, and stir until the components in the solution are completely dissolved in each other and become clear and transparent; Step 4: Add tetraethoxysilane TEOS to the solution obtained in step 3 in a volume ratio of 1:7 to 1:9 to ethylene carbonate EC, and stir until the components in the solution are completely miscible and clear and transparent.
2. The method for preparing a wide temperature range electrolyte for lithium-ion batteries according to claim 1, characterized in that: The method for preparing the wide temperature range electrolyte for lithium-ion batteries also includes step five: heating the mixed solution obtained in step four to 25° C., and adding vinyl carbonate (VC), diethylene sulfate (DTD) and fluoroethylene carbonate (FEC) in a volume ratio of 1:2:3-3:2:1 in sequence.
3. An energy storage device, characterized in that: It comprises a positive electrode, a negative electrode, a separator and an electrolyte, wherein the electrolyte is prepared by the preparation method of a wide temperature range electrolyte for lithium-ion batteries as claimed in claim 2, the positive electrode material is a lithium oxide mixed nanoporous activated carbon, and the negative electrode material is an amorphous carbon-based material hard carbon or soft carbon; the mass ratio of lithium tetrafluorophosphate (LiBF4) and lithium hexafluorophosphate (LiPF6) is 2:8; in the step 1, a magnetic particle is used to stir at a speed of 100 to 200 r / min for 1.5 h to 2 h until the three solvents are completely miscible and no stratification occurs.
4. The energy storage device according to claim 3, characterized in that: In the step 3, the concentration of the mixture of lithium tetrafluorophosphate (LiBF4) and lithium hexafluorophosphate (LiPF6) in the lithium salt is 1 mol / L.
5. The energy storage device according to claim 4, characterized in that: In the step 3, the rotation speed of the magnet is 200-300 r / min.
6. The energy storage device according to claim 5, characterized in that: In the step 4, the mass fraction of tetraethoxysilane (TEOS) is 0.5%, and the rotation speed of the magnet is 200-300 r / min.
7. The energy storage device according to claim 6, characterized in that: In the step 5, vinylene carbonate (VC), vinyl sulfate (DTD) and fluoroethylene carbonate (FEC) are added in sequence respectively, which needs to be carried out in 5 times, and the interval time of each time is controlled within 6 to 8 minutes, and the stirring speed is controlled at 300r / min.
8. The energy storage device according to claim 7, characterized in that: In the step 1, the volume ratio of ethylene carbonate (EC), ethyl butyrate (EB) and ethyl methyl carbonate (EMC) is 1:1:2, and in the step 5, the volume ratio of vinylene carbonate (VC), diethylene sulfate (DTD) and fluoroethylene carbonate (FEC) is 1:1.2:1.
5.
9. The energy storage device according to claim 8, characterized in that: The steps 1 to 5 are all performed in a glove box, and the oxygen concentration and water concentration are both less than 0.01 ppm.
10. The energy storage device according to claim 9, characterized in that: The separator is high molecular weight polyethylene and polypropylene.